The present invention relates to improvements in apparatus for mixing batches or charges of flowable solid materials, such as constituents of concrete, other building materials, fodder and others. More particularly, the invention relates to improvements in apparatus of the type wherein the mixing instrumentalities rotate about a substantially horizontal axis in a mixing chamber which is defined by a housing having two end walls, a tubular shell between the end walls and one or more doors which are movable between first and second positions to thereby respectively expose and close the opening. The opening allows for evacuation of the contents of the mixing chamber by gravity flow in response to movement of the door or doors to first position or positions.
In apparatus of the above outlined character, the opening is normally or often dimensioned in such a way that the contents of the mixing chamber can be evacuated by gravity flow regardless of the angle of repose of the batch of material which is treated in the apparatus. Also, the opening normally extends all the way between the end walls in order to ensure complete evacuation of the entire contents of the mixing chamber when the need arises. Reference may be had to German Offenlegungsschrift No. 32 36 780.
An important advantage of the apparatus which is disclosed in the German application is that the entire contents of the mixing chamber can be evacuated from the housing so that, if the batch which has undergone treatment contains only solid constituents, the interior of the housing need not be cleaned prior to introduction of the next batch. Thus, all that is necessary is to close the opening and to admit the constituents of the next batch.
French Pat. No. 1,329,058 discloses a mixing apparatus with a rotating housing which has a polygonal cross-sectional outline and whose opening can be closed by two doors resembling the jaws of a bucket. The arrangement is such that actual movement of the doors to open positions, in which the opening of the polygonal housing is exposed, must be preceded by a movement downwardly and away from the adjacent portions of the housing. Such downward movement of the doors is necessary in order to disengage them from sealing strips which surround the opening and must be engaged by the doors when the opening is closed. The next step involves a sidewise movement of the doors away from each other. The procedure is repeated in reverse when the opening is to be closed.
A drawback of the patented apparatus is that the door opening and closing mechanism is complex, bulky and expensive. Moreover, the area of the fully exposed opening is too small to ensure complete evacuation of the contents of the mixing chamber. Still further, the seals around the opening are positioned in such a way that they are contacted by the outflowing material which tends to deposit thereon and to thus prevent the establishment of a satisfactory sealing action. The inner sides of the doors carry upstanding strips which are supposed to bear against the sealing elements. Such strips and the external surfaces of the doors define groove-like recesses or compartments which allow for the accumulation of flowable solid materials in open positions of the doors. Therefore, the patented apparatus is not ideally suited for mixing of successive batches which contain different constituents because the housing, the seals, the doors and the strips on the doors must be cleaned prior to the mixing of a different batch.
Swiss Pat. No. 349,477 discloses a mixing apparatus with a stationary housing having a single door which is pivotable between open and closed positions. The manner in which the door is to sealingly engage the housing around the opening is not disclosed and/or shown. Also, the patent does not disclose whether or not the opening is large enough to allow for the evacuation of the entire contents of the mixing chamber which is intended to receive the constituents of fodder or the like.
All types of apparatus for mixing flowable solid constituents must be adequately sealed in actual use because the mixing chamber is normally maintained at an elevated pressure. The pressure is very high when the apparatus is relatively large so that it can turn out successive batches containing large quantities of intermixed solid constituents. Therefore, the trend in the relevant industries is to provide the housing of mixing apparatus with relatively small openings which can be more readily sealed prior to start of and in the course of a mixing operation. This, of course, presents problems in connection with the evacuation of the contents of the mixing chamber and renders it necessary to clean the apparatus prior to the making of a different batch, i.e., a batch containing ingredients different from those in the preceding batch.